Electrochemical devices, such as proton exchange membrane fuel cells, sensors, electrolyzers, chlor-alkali separation membranes, and the like, have been constructed from membrane electrode assemblies (MEAs). An MEA used in a typical electrochemical cell, for example, includes an ion conductive membrane (ICM) that is in contact with an anode and a cathode. The anode/membrane/cathode structure is sandwiched between two microporous, electrically conductive elements called diffusion current collectors (DCCs) to form a five layer MEA. Ions formed at the anode are transported to the cathode, allowing current to flow in an external circuit connecting the electrodes.
The ICM typically comprises a polymeric electrolyte material, which may constitute its own structural support or may be contained in a porous structural membrane. Cation- or proton-transporting polymeric electrolyte materials may be salts of polymers containing anionic groups and are often partially or completely fluorinated.
Fuel cell MEAs have been constructed using catalyst electrodes in the form of applied dispersions of either Pt or carbon supported Pt catalysts. A catalyst form used for polymer electrolyte membranes is Pt or Pt alloys coated onto larger carbon particles by wet chemical methods, such as reduction of chloroplatnic acid. This form of catalyst is dispersed with ionomeric binders, solvents, and often polytetrafluoroethylene (PTFE) particles to form an ink, paste, or dispersion that is applied either to the membrane or the DCCs.
More recently, catalyst layers have been formed using nanostructured support elements bearing particles or nanostructured thin films (NSTF) of catalytic material. The nanostructured catalyst electrodes may be incorporated into very thin surface layers of the ICM forming a dense distribution of catalyst particles. The use of nanostructured thin film (NSTF) catalyst layers allows much higher catalyst utilization than catalyst layers formed by dispersion methods.
The present invention describes methods for making enhanced catalyst layers used for electrochemical devices and offers various advantages over the prior art.